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I. Liska (IACS/CUA)
An analysis of physical processes in the circumstellar material swept up and enveloped in the expanding shockfront of a supernova remnant is ideally represented by a hydrodynamic treatment of the fluid flows. Nevertheless, a LaGrangian treatment of the bulk kinematics of a shock-driven shell yields a useful and instructive set of approximate equations that relate the shell's basic dynamical variables and structural features. A description of the shock-driven outer shell of the displaced interstellar medium, buoyed from within by the thermal pressure of ejected coronal gas filling an internal cavity region, can be obtained. This approach is an attempt to extract the most from fundamental conservation principles, namely the conservation of energy for an adiabatic expansion, as well as the conservation of mass and momentum of the displaced interstellar matter across the junction interface of the shockfront. The basic LaGrangian employed represents an outer shell region in a dynamically stable state and in hydrostatic equilibrium. This representation is made possible by assuming that the post-shock deceleration of the gas flow acts as an effective outward gravitational force counter-balancing a positive pressure gradient directed toward the high density surface of the expanding envelope.